1. Field of the Invention
The present invention relates to the manufacture of vehicle doors.
2. Background Art
Conventional vehicle doors are generally stamped from steel blanks in a press forming line including a first drawing step followed by trimming, flanging, and piercing operations. Normally, an inner door panel and an outer door panel are formed in separate stamping operations. The inner and outer door panels are then assembled together with reinforcement bars, brackets and other components. It is not unusual for a conventional vehicle door to have as many as 20 pieces in the completed assembly.
Doors made by a stamping process are limited by manufacturing constraints to relatively shallow contours and are limited to the extent that feature lines may be formed in the door panels. For example, stamped doors cannot be made with feature lines that originate in a flat surface at the middle of a panel.
Conventional vehicle doors made with a large number of pieces tend to suffer from a lack of dimensional control due to the stack up of tolerances permitted for each part. Poor dimensional control adversely impacts vehicle craftsmanship and quality assessment target achievement. Parts are made within a certain degree of dimensional tolerance but when additional parts are assembled together, the tolerances may accumulate making it difficult to control the final dimensional tolerances of the finished door assembly.
It has been proposed to manufacture vehicle doors from aluminum to save weight. Aluminum doors made in a conventional stamping line must generally be manufactured from aluminum sheet that is less than 0.9 mm in thickness. If thicker aluminum sheet is used, excessive splitting and cracking may occur especially in tight radius bends. Door inner and outer panels made with 0.9 mm aluminum are too thin generally to accept mounting hardware without additional reinforcement.
Super-plastic forming (SPF) technology has been used in the manufacture of vehicles including the manufacture of decklids and hoods. In one such door, aluminum having a thickness of 0.9 mm is super-plastic formed and a cast hinge plate and cast striker plate are secured to reinforce the door mounting hardware.
It has also been proposed to use thermally cured adhesives to aid in securing panels of vehicle parts together. Thermally cured adhesives may shift when heated in an oven. Any shift in the position of the door inner relative to the door outer can result in unacceptable dimensional variation.
There is a need for a lightweight vehicle door structure that does not require added reinforcements other than those integrally formed in the inner door panel. Adding reinforcements increases the weight of the overall door assembly.
Further, vehicle fit and finish requirements for world class vehicle manufacturing demand dimensional control of the inner and outer door panels to within 1 mm and of the assembled door inner and outer to be less than 1.25 mm. There is also a need for a manufacturing process that permits wider latitude in design shape and feature line capability.
It would be desirable to reduce the total part count by eliminating reinforcements, such as door hinge and latch reinforcements, and at the same time there is a need for greater dimensional control. Further, there is a need for a vehicle door that does not distort or shift in position when exposed to heat during electro-coat processes and in paint ovens.
These and other problems and needs are addressed by applicants' invention as summarized below.